For the purposes of the present invention, reference is made to the following definitions.
The “media type” of a connection between terminals associated to corresponding users refers to the typology of the content exchanged by the users by means of the connection, which can typically be audio or data. As an example, audio comprises voice (e.g. speech) or music; data comprise at least one of the following contents: images (e.g., moving images such as a video, or still images such as pictures), files, electronic documents, or software applications. With the expression “a connection of a “X” media type” (e.g. audio or data) it is meant that the connection supports and/or allows exchanging of the “X” media type (e.g. audio or data).
With the term “connection of the multimedia type” it is meant a single connection (i.e. a single transmission channel, technique and/or protocol, for example, on a packet or circuit domain) between terminals associated to corresponding users, which supports and/or allows the users to exchange content of more than one media type in the same session, e.g. content comprising both data content and audio content. As an example, a videocall is a multimedia type connection.
Particularly, multimedia type connections have been offered by third generation systems such as UMTS (Universal Mobile Telecommunications System), wherein terminals support videocalls on a circuit channel having a transmission rate of 64 Kbit's. The third generation technology UMTS is based on a W-CDMA technique (WideBand-Code Division Multiple Access).
It has to be noticed that the evolution from the earlier mobile communications systems generations (i.e. first an second generations) to the third generation ones has not yet been completed and, probably, systems of earlier generations will be always maintained together with the systems of the current generation.
With particular reference to videocalls, systems and/or terminals supporting “combinational sessions” can provide users with a service analogous to the videocall but based on non-multimedia type connections and, as an example, based on second generation systems (GSM/GPRS). By the term “combinational session” herein is generally meant a communication session enjoyable through two or more connections at the same time. The connections may be based on different network domains, such as the packet domain and the circuit domain. Particularly, services employing combinational sessions (i.e. combinational services) are typically performed by establishing a first connection of a first media type (such as, for example, a voice connection) and a separated second connection of a different second media type (such as, for example, a video connection) at the same time.
U. Olsson and M. Nilsson, in the article entitled “Combinational services—The pragmatic first step toward all-IP”, Ericsson Review No. 2, 2003, describe, inter alia, an example of the so-called “combinational services” in which the possibility is exploited of managing traffic in both circuit connection and packet connection at the same time: image sharing during a conversation between two users. The authors note that traffic can be simultaneously managed in a circuit connection and packet connection both with Wideband Code Division Multiple Access (WCDMA), which allows using multiple and parallel bearers in the “over-the-air” interface (multiple radio access bearers, multi-RAB) and with GSM, in which similar possibilities are offered by a standardized mechanism—the dual transfer mode, DTM.
Another description of a service that can be employed by means of mobile terminals, similar to that discussed above, is given in White Paper “Video sharing—Enrich your voice call with video”, by Nokia Corporation, which is available for download at                http:/www.nokia.com/BaseProject/Site s/NOKIA_MAIN—18022/CDA/Categories/Phones/TechnologiesNideoSharing/_Content/_Static_Files/video_sharing_a4—2510.pdfThe real-time video sharing service allows two users to easily enrich their communication during a telephone conversation. Either of the users can share a live video recorded by a video camera, or video clips on his/her terminal. Both users watch the same video and can discuss the latter while continuing their voice call.        
Document WO-A-2004/084457 describes a method for establishing communication between a first wireless terminal supporting audio and video calls and a second wireless terminal supporting audiocalls but not videocalls. According to this method, the first wireless terminal requests to establish a communication with the second terminal. A management module checks whether the second wireless terminal has a video capability and as the second terminal is voice capable only, the call request is sent to a video gateway which sets up a video session between the first wireless terminal and a video server. The video server generates and sends video or picture to the video gateway for transmission to the user of the first wireless terminal. The video or the picture indicates to the user of the first wireless terminal that a voice call is being established between first and second wireless terminals. Moreover, in the above described situation the communication between the first and second wireless terminal can be ended or only a non video session is set up establishing a voice channel between the terminals.
Document EP-A-1148688 discloses a proxy apparatus that allows for communication session set up according to different communication capability. The proxy apparatus receives a request for a communication session originated from a first subscriber using a first group of terminal such as a mobile telephone and a data terminal. The request identifies a second subscriber associated to a multimedia Personal Computer. The proxy apparatus evaluates data and speech as types of communication being available for the first group of terminal and multimedia as types of communication being available for the multimedia Personal Computer. Then, the proxy apparatus sets up terminal sub-session between the groups of terminals available according to types of communication being available. The communication between the terminals above indicated requires merging data and speech into a multimedia data stream for submission to the Personal Computer and splitting of the multimedia data stream into single speech and data streams to be submitted to the mobile telephone and the data terminal.